Is my water pressure too high?

[DarkPedals]

I have what I believe to be a fully working Sime Super 90 plus boiler. It heats the CH and it heat the DHW fine (the diverter valve is working because when the CH is off, the hot water heats up).

BUT, if I open my main stop tap fully, the water pressure is such that the boiler can't cope - at best it makes the hot water tepid but it's only really marginally slightly warmer than freezing (especially at this time of year). My solution is to close the stop tap to lower the pressure - eventually I find a balance where the boiler can heat the hot water enough to make it too hot to hold you hand under.

So, what's my problem? Is my water pressure too high? Should the boiler restrict the water flow so it only passes what it can cope with? Is the boiler simply underpowered for the job?

Thanks,

Bob

 

[kevplumb]

pressure aint the problem flowrate is

 

[meldrew's_mate]

Try turning the taps down so the flowrate is the same as it was with the stopcock nearly closed. Higher flowrates mean cooler water, it's under your control

 

[Softus]

My solution is to close the stop tap to lower the pressure - eventually I find a balance where the boiler can heat the hot water enough to make it too hot to hold you hand under.

Surely you can achieve the same effect by not opening the hot tap very much? If so then why fiddle with the stop cock? If not, then something odd is happening.

 

[oilman]

The boiler probably meets its spec, and will be no problem in the summer. Winter is colder, and so is the water supply, so to get it hot takes more effort in winter than summer. You could fit a flow restrictor, and many boilers have one fitted anyway. First though, you need to measure the flow through the hot tap with it fully open. What is the flow rate?

 

[DarkPedals]

Thanks all, I didn't expect so many replies so quickly!

OK, I need to clear up a couple of things - I didn't mention this before because I didn't want to overcomplicated things....

The hot water isn't actually a problem, but from my very small previous experience it normal heats up quicker and better than it does at the moment.

The actual problem is my thermostatic shower - when my stop tap is opened fully, the shower won't get hot - yes, it's nice and powerful, but it's blo0dy freezing. This is why I started lowering my flowrate via the stop tap. I've had a few discussions with the shower manufacturer and they want to know 'what water pressure is running to the shower' - how do I find *this* out?

Finally - Oilman - how do I measure my flowrate - is it a case of 'it'll fill a 10 litre bucket in X seconds'?

Thanks again all,

Bob

 

[ChrisR]

I've had a few discussions with the shower manufacturer and they want to know 'what water pressure is running to the shower'

They've asked you that because they're incompetent, stupid, lazy and not fit to answer a telephone let alone queries about their own products. Pressure does not "run".

The above posters are are of course correct - you haven't quite grasped it yet! If the flow rate through the boiler is too high, it won't be able to get much energy into each litre, say, so you have tepid water. All the shower can do is let it through, it can't make it hotter - it doesn't "know" that if it restricted the hot flow that the hot would get hotter, it just opens the hot side fully.

Yes fill a 10 litre bucket. You should expect, with mains temperatures as cold as they are at the moment, 10 litres of shower-temperature water in around 75 seconds from a 24kW/ 80,000Btu/hr boiler.

There will be a quarter-turn type tap on the cold input to the boiler. Turn it so that the flow through thr boiler is 8 lires/minute. It might be a bit noisy. It might also weep for a while but they usually stop eventually.

 

[DarkPedals]

Cheers Chris,

Right! I'm getting somewhere now. Sort of.

Before we get hung up with the problems I'm having with the shower, I want to look at my DHW only. Here's my situation:

I've turn the mains stop tap to *fully* open. I've played with the quarter-turn tap on the cold water inlet for the boiler down so that when my hot tap is fully on in the kitchen sink the water is too hot to hold your hand under. I'm not sure what temp this is because my digital thermometer maxes out at 45 oC!!! So, here's my next question....

Looking at DHW only, is there a figure as to what my boiler should be able to sustain? At the hot temp mentioned about, I'm filling 10 litres in about 2.05 minutes. My cold water is filling 10 litres in just under 30 seconds!

I've just found some info which says my boiler outputs DHW at 26.4 kW / 90,000 Btu/h.

Two more quick things - yes, I'm convinced the people at the show manufacturers are useless. Also, I apologise for confusing water pressure and flow rate - my mum (a Physics teacher) would kill me if she knew... and I got an A for Physics GSCE but it was a while ago now.....

Thanks (yet) again,

Bob

 

[DarkPedals]

One more quick thing which I've just noticed....

Once the CH is turned off and boiler the flow and return pipes have gone cold, if I run DHW for long enough to get truely hot (about a minute), the CH flow pipe also gets very hot.

Is this right, or does it mean that there's something wrong with my NEW diverter valve?

Thanks,

Bob